1. Field of the Invention
The present invention relates to an ink ribbon cassette for use in a serial printer.
2. Description of the Related Art
There have heretofore been employed ink ribbon cassettes each comprising an endless ink ribbon housed in a box-shaped cassette, the ink ribbon cassette being mounted on a printer carriage in use. The ink ribbon cassette of this construction is advantageous in that it can easily be installed on the printer carriage, it will not smear the operator's hands and surrounding parts when it is installed on the carriage, and it is small in size. One example of ink ribbon cassette is shown in U.S. Pat. No. 4,383,775.
The known ink ribbon cassette generally has a pair of laterally spaced ribbon guide arms with a space left therebetween for positioning and a print head therein. The endless ribbon accommodated in the ink ribbon cassette runs out of one of the ink ribbon arms and returns into the other ink ribbon arm. During printing, the print head employs an exposed portion of the ink ribbon as it runs between the ribbon guide arms for printing desired characters. Since the ink ribbon is endless, the ink ribbon is fed in circulation to renew the exposed ribbon portion continuously for printing.
When the ink ribbon cassette is installed in the printer, the print head is positioned in the space defined between the ribbon guide arms. In operation, the print head hits the exposed ink ribbon portion to print characters or the like on a sheet of print paper against a platen disposed in confronting relation to the ink ribbon.
If there is an obstruction such as a mass of dust in the print head or on the sheet, then the ink ribbon will tend to sag or the sheet will be likely to be smeared. The ink ribbon may be caught by perforations in the sheet, with the result that the ink ribbon may not be fed smoothly or may be jammed.
One prior solution to the above problem has been to use a ribbon protector between the sheet and the ink ribbon. It has been customary to mount the ribbon protector by fixing it in slits in the ink ribbon cassette or bonding it to the ink ribbon cassette. U.S. Pat. No. 4,383,775 also discloses an ink ribbon cassette with such a ribbon protector.
Where the ribbon protector is fixed to the ink ribbon cassette, the ribbon protector is rendered positionally immovable between the ink ribbon and the sheet, and hence should be positioned highly accurately. Therefore, it has been time-consuming and laborious to mount the ribbon protector on the ink ribbon cassette, and the attached ribbon protector could not easily be replaced with a new one.